Worst-Case Analysis of the X-38 Crew Return Vehicle Flight Control System

Abstract

A linear fractional transformation (LFT) model of the linearized equation of the lateral-directional axes of the X-38 crew return vehicle is developed to facilitate the analysis of e ight control systems. The LFT model represents uncertainty in nine aerodynamic stability derivatives at a given e ight condition with frequency-domain performance specie cations. The X-38 LFT model combined with a controller at specie c e ight conditions is used to determine the aerodynamic coefe cients that result in the worst-case performance and gain/phase margin of the closed-loop system. The objective is to verify that a given controller remains stable and achieves desired performance objectives for all predee ned aerodynamic variations at select operating conditions along its e ight trajectory.